Provided by: libdancer2-perl_0.400001+dfsg-1_all 
NAME
Dancer2::Manual - A gentle introduction to Dancer2
VERSION
version 0.400001
DESCRIPTION
Dancer2 is a free and open source web application framework written in Perl.
It's a complete rewrite of Dancer, based on Moo and using a more robust and extensible
fully-OO design.
It's designed to be powerful and flexible, but also easy to use - getting up and running
with your web app is trivial, and an ecosystem of adaptors for common template engines,
session storage, logging methods, serializers, and plugins to make common tasks easy means
you can do what you want to do, your way, easily.
INSTALL
Installation of Dancer2 is simple, using your favourite method to install from CPAN, e.g.:
perl -MCPAN -e 'install Dancer2'
Thanks to the magic of cpanminus, if you do not have CPAN.pm configured, or just want a
quickfire way to get running, the following should work, at least on Unix-like systems:
wget -O - http://cpanmin.us | sudo perl - Dancer2
(If you don't have root access, omit the 'sudo', and cpanminus will install Dancer2 and
prereqs into "~/perl5".)
Dancer2 is also available as a package from the package repository of several
distributions, for example on Debian/Ubuntu you should be able to just:
apt-get install libdancer2-perl
Do be aware, though, that distribution-packaged versions sometimes lag behind the most
recent version on CPAN.
BOOTSTRAPPING A NEW APP
Create a web application using the dancer script:
$ dancer2 gen -a MyApp && cd MyApp
+ MyApp
+ MyApp/config.yml
+ MyApp/Makefile.PL
+ MyApp/MANIFEST.SKIP
+ MyApp/.dancer
+ MyApp/cpanfile
+ MyApp/bin
+ MyApp/bin/app.psgi
+ MyApp/environments
+ MyApp/environments/development.yml
+ MyApp/environments/production.yml
+ MyApp/lib
+ MyApp/lib/MyApp.pm
+ MyApp/public
+ MyApp/public/favicon.ico
+ MyApp/public/500.html
+ MyApp/public/dispatch.cgi
+ MyApp/public/404.html
+ MyApp/public/dispatch.fcgi
+ MyApp/public/css
+ MyApp/public/css/error.css
+ MyApp/public/css/style.css
+ MyApp/public/images
+ MyApp/public/images/perldancer.jpg
+ MyApp/public/images/perldancer-bg.jpg
+ MyApp/public/javascripts
+ MyApp/public/javascripts/jquery.js
+ MyApp/t
+ MyApp/t/001_base.t
+ MyApp/t/002_index_route.t
+ MyApp/views
+ MyApp/views/index.tt
+ MyApp/views/layouts
+ MyApp/views/layouts/main.tt
It creates a directory named after the name of the app, along with a configuration file, a
views directory (where your templates and layouts will live), an environments directory
(where environment-specific settings live), a module containing the actual guts of your
application, and a script to start it. A default skeleton is used to bootstrap the new
application, but you can use the "-s" option to provide another skeleton. For example:
$ dancer2 gen -a MyApp -s ~/mydancerskel
For an example of a skeleton directory check the default one available in the "share/"
directory of your Dancer2 distribution.
(In what follows we will refer to the directory in which you have created your Dancer2
application -- e.g., what "MyApp" was above -- as the "appdir".)
Because Dancer2 is a PSGI web application framework, you can use the "plackup" tool
(provided by Plack) for launching the application:
plackup -p 5000 bin/app.psgi
View the web application at:
http://localhost:5000
USAGE
When Dancer2 is imported to a script, that script becomes a webapp, and at this point, all
the script has to do is declare a list of routes. A route handler is composed by an HTTP
method, a path pattern and a code block. "strict", "warnings" and "utf8" pragmas are also
imported with Dancer2.
The code block given to the route handler has to return a string which will be used as the
content to render to the client.
Routes are defined for a given HTTP method. For each method supported, a keyword is
exported by the module.
HTTP Methods
Here are some of the standard HTTP methods which you can use to define your route
handlers.
• GET The GET method retrieves information, and is the most common
GET requests should be used for typical "fetch" requests - retrieving information.
They should not be used for requests which change data on the server or have other
effects.
When defining a route handler for the GET method, Dancer2 automatically defines a
route handler for the HEAD method (in order to honour HEAD requests for each of your
GET route handlers).
To define a GET action, use the get keyword.
• POST The POST method is used to create a resource on the server.
To define a POST action, use the post keyword.
• PUT The PUT method is used to replace an existing resource.
To define a PUT action, use the put keyword.
a PUT request should replace the existing resource with that specified - for instance
- if you wanted to just update an email address for a user, you'd have to specify all
attributes of the user again; to make a partial update, a PATCH request is used.
• PATCH The PATCH method updates some attributes of an existing resource.
To define a PATCH action, use the patch keyword.
• DELETE The DELETE method requests that the origin server delete the resource
identified by the Request-URI.
To define a DELETE action, use the del keyword.
Handling multiple HTTP request methods
Routes can use "any" to match all, or a specified list of HTTP methods.
The following will match any HTTP request to the path "/myaction":
any '/myaction' => sub {
# code
}
The following will match GET or POST requests to "/myaction":
any ['get', 'post'] => '/myaction' => sub {
# code
};
For convenience, any route which matches GET requests will also match HEAD requests.
Route Handlers
The route action is the code reference declared. It can access parameters through the
specific route_parameters, query_parameters, and body_parameters keywords, which return a
Hash::MultiValue object. This hashref is a merge of the route pattern matches and the
request params.
You can find more details about how params are built and how to access them in the
Dancer2::Core::Request documentation.
Declaring Routes
To control what happens when a web request is received by your webapp, you'll need to
declare "routes". A route declaration indicates which HTTP method(s) it is valid for, the
path it matches (e.g. "/foo/bar"), and a coderef to execute, which returns the response.
get '/hello/:name' => sub {
return "Hi there " . route_parameters->get('name');
};
The above route specifies that, for GET requests to "/hello/...", the code block provided
should be executed.
Retrieving request parameters
The query_parameters, route_parameters, and body_parameters keywords provide a
Hash::MultiValue result from the three different parameters.
Named matching
A route pattern can contain one or more tokens (a word prefixed with ':'). Each token
found in a route pattern is used as a named-pattern match. Any match will be set in the
route parameters.
get '/hello/:name' => sub {
return "Hey " . route_parameters->get('name') . ", welcome here!";
};
Tokens can be optional, for example:
get '/hello/:name?' => sub {
my $name = route_parameters->get('name') // 'Whoever you are';
return "Hello there, $name";
};
Named matching with type constraints
Type constraints can be added to tokens.
get '/user/:id[Int]' => sub {
# matches /user/34 but not /user/jamesdean
my $user_id = route_parameters->get('id');
};
get '/user/:username[Str]' => sub {
# matches /user/jamesdean but not /user/34 since that is caught
# by previous route
my $username = route_parameters->get('username');
};
You can even use type constraints to add a regexp check:
get '/book/:date[StrMatch[qr{\d\d\d\d-\d\d-\d\d}]]' => sub {
# matches /book/2014-02-04
my $date = route_parameters->get('date');
};
The default type library is Dancer2::Core::Types but any type library built using
Type::Tiny's Type::Library can be used instead. If you'd like to use a different default
type library you must declare it in the configuration file, for example:
type_library: My::Type::Library
Alternatively you can specify the type library in which the type is defined as part of the
route definition:
get '/user/:username[My::Type::Library::Username]' => sub {
my $username = route_parameters->get('username');
};
This will load "My::Type::Library" and from it use the type "Username". This allows types
to be used that are not part of the type library defined by config's "type_library".
More complex constructs are allowed such as:
get '/some/:thing[Int|MyDate]' => sub {
...;
};
See "lookup($name)" in Type::Registry for more details.
Wildcard Matching
A route can contain a wildcard (represented by a "*"). Each wildcard match will be placed
in a list, which the "splat" keyword returns.
get '/download/*.*' => sub {
my ($file, $ext) = splat;
# do something with $file.$ext here
};
An extensive, greedier wildcard represented by "**" (A.K.A. "megasplat") can be used to
define a route. The additional path is broken down and returned as an arrayref:
get '/entry/*/tags/**' => sub {
my ( $entry_id, $tags ) = splat;
my @tags = @{$tags};
};
The "splat" keyword in the above example for the route /entry/1/tags/one/two would set
$entry_id to 1 and $tags to "['one', 'two']".
Mixed named and wildcard matching
A route can combine named (token) matching and wildcard matching. This is useful when
chaining actions:
get '/team/:team/**' => sub {
var team => route_parameters->get('team');
pass;
};
prefix '/team/:team';
get '/player/*' => sub {
my ($player) = splat;
# etc...
};
get '/score' => sub {
return score_for( vars->{'team'} );
};
Regular Expression Matching
A route can be defined with a Perl regular expression.
In order to tell Dancer2 to consider the route as a real regexp, the route must be defined
explicitly with "qr{}", like the following:
get qr{/hello/([\w]+)} => sub {
my ($name) = splat;
return "Hello $name";
};
A route regex may use named capture groups. The "captures" keyword will return a reference
to a copy of "%+".
Conditional Matching
Routes may include some matching conditions (on content_type, agent, user_agent,
content_length and path_info):
get '/foo', {agent => 'Songbird (\d\.\d)[\d\/]*?'} => sub {
'foo method for songbird'
}
get '/foo' => sub {
'all browsers except songbird'
}
Prefix
A prefix can be defined for each route handler, like this:
prefix '/home';
From here, any route handler is defined to /home/*
get '/page1' => sub {}; # will match '/home/page1'
You can unset the prefix value
prefix '/'; # or: prefix undef;
get '/page1' => sub {}; # will match /page1
Alternatively, to prevent you from ever forgetting to undef the prefix, you can use
lexical prefix like this:
prefix '/home' => sub {
get '/page1' => sub {}; # will match '/home/page1'
}; ## prefix reset to previous value on exit
get '/page1' => sub {}; # will match /page1
Delayed responses (Async/Streaming)
Dancer2 can provide delayed (otherwise known as asynchronous) responses using the
"delayed" keyword. These responses are streamed, although you can set the content all at
once, if you prefer.
get '/status' => sub {
delayed {
response_header 'X-Foo' => 'Bar';
# flush headers (in case of streaming)
flush;
# send content to the user
content 'Hello, world!';
# you can write more content
# all streaming
content 'Hello, again!';
# when done, close the connection
done;
# do whatever you want else, asynchronously
# the user socket closed by now
...
};
};
If you are streaming (calling "content" several times), you must call "flush" first. If
you're sending only once, you don't need to call "flush".
Here is an example of using delayed responses with AnyEvent:
use Dancer2;
use AnyEvent;
my %timers;
my $count = 5;
get '/drums' => sub {
delayed {
print "Stretching...\n";
flush; # necessary, since we're streaming
$timers{'Snare'} = AE::timer 1, 1, delayed {
$timers{'HiHat'} ||= AE::timer 0, 0.5, delayed {
content "Tss...\n";
};
content "Bap!\n";
if ( $count-- == 0 ) {
%timers = ();
content "Tugu tugu tugu dum!\n";
done;
print "<enter sound of applause>\n\n";
$timers{'Applause'} = AE::timer 3, 0, sub {
# the DSL will not available here
# because we didn't call the "delayed" keyword
print "<applause dies out>\n";
};
}
};
};
};
If an error happens during a write operation, a warning will be issued to the logger.
You can handle the error yourself by providing an "on_error" handler:
get '/' => sub {
delayed {
flush;
content "works";
# ... user disconnected here ...
content "fails";
# ... error triggered ...
done; # doesn't even get run
} on_error => sub {
# delayed{} not needed, DSL already available
my ($error) = @_;
# do something with $error
};
};
Here is an example that asynchronously streams the contents of a CSV file:
use Dancer2;
use Text::CSV_XS qw< csv >;
use Path::Tiny qw< path >;
use JSON::MaybeXS qw< encode_json >;
# Create CSV parser
my $csv = Text::CSV_XS->new({
binary => 1,
auto_diag => 1,
});
get '/' => sub {
# delayed response:
delayed {
# streaming content
flush;
# Read each row and stream it in JSON
my $fh = path('filename.csv')->openr_utf8;
while ( my $row = $csv->getline($fh) ) {
content encode_json $row;
}
# close user connection
done;
} on_error => sub {
my ($error) = @_;
warning 'Failed to stream to user: ' . request->remote_address;
};
};
NOTE: If you just want to send a file's contents asynchronously, use
"send_file($filename)" instead of "delayed", as it will automatically take advantage of
any asynchronous capability.
Action Skipping
An action can choose not to serve the current request and ask Dancer2 to process the
request with the next matching route.
This is done with the pass keyword, like in the following example
get '/say/:word' => sub {
pass if route_parameters->get('word') =~ /^\d+$/;
"I say a word: " . route_parameters->get('word');
};
get '/say/:number' => sub {
"I say a number: " . route_parameters->get('number');
};
HOOKS
Hooks are code references (or anonymous subroutines) that are triggered at specific
moments during the resolution of a request. They are set up using the hook keyword.
Many of them are provided by Dancer2's core, but plugins and engines can also define their
own.
• "before" hooks
"before" hooks are evaluated before each request within the context of the request and
receives as argument the app (a Dancer2::Core::App object).
It's possible to define variables which will be accessible in the action blocks with
the var keyword.
hook before => sub {
var note => 'Hi there';
};
get '/foo/*' => sub {
my ($match) = splat; # 'oversee';
vars->{note}; # 'Hi there'
};
For another example, this can be used along with session support to easily give non-
logged-in users a login page:
hook before => sub {
if (!session('user') && request->path !~ m{^/login}) {
# Pass the original path requested along to the handler:
forward '/login', { requested_path => request->path };
}
};
The request keyword returns the current Dancer2::Core::Request object representing the
incoming request.
• "after" hooks
"after" hooks are evaluated after the response has been built by a route handler, and
can alter the response itself, just before it's sent to the client.
This hook runs after a request has been processed, but before the response is sent.
It receives a Dancer2::Core::Response object, which it can modify if it needs to make
changes to the response which is about to be sent.
The hook can use other keywords in order to do whatever it wants.
hook after => sub {
response->content(
q{The "after" hook can alter the response's content here!}
);
};
Templates
• "before_template_render"
"before_template_render" hooks are called whenever a template is going to be
processed, they are passed the tokens hash which they can alter.
hook before_template_render => sub {
my $tokens = shift;
$tokens->{foo} = 'bar';
};
The tokens hash will then be passed to the template with all the modifications
performed by the hook. This is a good way to setup some global vars you like to have
in all your templates, like the name of the user logged in or a section name.
• "after_template_render"
"after_template_render" hooks are called after the view has been rendered. They
receive as their first argument the reference to the content that has been produced.
This can be used to post-process the content rendered by the template engine.
hook after_template_render => sub {
my $ref_content = shift;
my $content = ${$ref_content};
# do something with $content
${$ref_content} = $content;
};
• "before_layout_render"
"before_layout_render" hooks are called whenever the layout is going to be applied to
the current content. The arguments received by the hook are the current tokens hashref
and a reference to the current content.
hook before_layout_render => sub {
my ($tokens, $ref_content) = @_;
$tokens->{new_stuff} = 42;
$ref_content = \"new content";
};
• "after_layout_render"
"after_layout_render" hooks are called once the complete content of the view has been
produced, after the layout has been applied to the content. The argument received by
the hook is a reference to the complete content string.
hook after_layout_render => sub {
my $ref_content = shift;
# do something with ${ $ref_content }, which reflects directly
# in the caller
};
Error Handling
Refer to Error Hooks for details about the following hooks:
• "init_error"
• "before_error"
• "after_error"
• "on_route_exception"
File Rendering
Refer to File Handler for details on the following hooks:
• "before_file_render"
• "after_file_render"
Serializers
• "before_serializer" is called before serializing the content, and receives the content
to serialize as an argument.
hook before_serializer => sub {
my $content = shift;
...
};
• "after_serializer" is called after the payload has been serialized, and receives the
serialized content as an argument.
hook after_serializer => sub {
my $serialized_content = shift;
...
};
HANDLERS
File Handler
Whenever a content is produced out of the parsing of a static file, the
Dancer2::Handler::File component is used. This component provides two hooks,
"before_file_render" and "after_file_render".
"before_file_render" hooks are called just before starting to parse the file, the hook
receives as its first argument the file path that is going to be processed.
hook before_file_render => sub {
my $path = shift;
};
"after_file_render" hooks are called after the file has been parsed and the response
content produced. It receives the response object (Dancer2::Core::Response) produced.
hook after_file_render => sub {
my $response = shift;
};
Auto page
Whenever a page that matches an existing template needs to be served, the
Dancer2::Handler::AutoPage component is used.
Writing your own
A route handler is a class that consumes the Dancer2::Core::Role::Handler role. The class
must implement a set of methods: "methods", "regexp" and "code" which will be used to
declare the route.
Let's look at Dancer2::Handler::AutoPage for example.
First, the matching methods are "get" and "head":
sub methods { qw(head get) }
Then, the "regexp" or the path we want to match:
sub regexp { '/:page' }
Anything will be matched by this route, since we want to check if there's a view named
with the value of the "page" token. If not, the route needs to "pass", letting the
dispatching flow to proceed further.
sub code {
sub {
my $app = shift;
my $prefix = shift;
my $template = $app->template_engine;
if ( !defined $template ) {
$app->response->has_passed(1);
return;
}
my $page = $app->request->path;
my $layout_dir = $template->layout_dir;
if ( $page =~ m{^/\Q$layout_dir\E/} ) {
$app->response->has_passed(1);
return;
}
# remove leading '/', ensuring paths relative to the view
$page =~ s{^/}{};
my $view_path = $template->view_pathname($page);
if ( ! $template->pathname_exists( $view_path ) ) {
$app->response->has_passed(1);
return;
}
my $ct = $template->process( $page );
return ( $app->request->method eq 'GET' ) ? $ct : '';
};
}
The "code" method passed the Dancer2::Core::App object which provides access to anything
needed to process the request.
A "register" is then implemented to add the route to the registry and if the "auto_page
setting" is off, it does nothing.
sub register {
my ($self, $app) = @_;
return unless $app->config->{auto_page};
$app->add_route(
method => $_,
regexp => $self->regexp,
code => $self->code,
) for $self->methods;
}
The config parser looks for a "route_handlers" section and any handler defined there is
loaded. Thus, any random handler can be added to your app. For example, the default
config file for any Dancer2 application is as follows:
route_handlers:
File:
public_dir: /path/to/public
AutoPage: 1
ERRORS
Error Pages
When an HTTP error occurs (i.e. the action responds with a status code other than 200),
this is how Dancer2 determines what page to display.
• Looks in the "views/" directory for a corresponding template file matching the error
code (e.g. "500.tt" or "404.tt"). If such a file exists, it's used to report the
error.
• Next, looks in the "public/" directory for a corresponding HTML file matching the
error code (e.g. "500.html" or "404.html"). If such a file exists, it's used to report
the error. (Note, however, that if show_stacktrace is set to true, in the case of a
500 error the static HTML page will not be shown, but will be replaced with a default
error page containing more informative diagnostics. For more information see
Dancer2::Config.)
(In older versions, show_errors was used instead of show_stacktrace. Both are
supported, but show_errors is deprecated.)
• As default, render a generic error page on the fly.
Execution Errors
When an error occurs during the route execution, Dancer2 will render an error page with
the HTTP status code 500.
It's possible either to display the content of the error message or to hide it with a
generic error page. This is a choice left to the end-user and can be controlled with the
show_stacktrace setting (see above).
Error Hooks
When an error is caught by Dancer2's core, an exception object is built (of the class
Dancer2::Core::Error). This class provides a hook to let the user alter the error workflow
if needed.
"init_error" hooks are called whenever an error object is built, the object is passed to
the hook.
hook init_error => sub {
my $error = shift;
# do something with $error
};
This hook was named before_error_init in Dancer, both names currently are synonyms for
backward-compatibility.
"before_error" hooks are called whenever an error is going to be thrown, it receives the
error object as its sole argument.
hook before_error => sub {
my $error = shift;
# do something with $error
};
This hook was named before_error_render in Dancer, both names currently are synonyms for
backward-compatibility.
"after_error" hooks are called whenever an error object has been thrown, it receives a
Dancer2::Core::Response object as its sole argument.
hook after_error => sub {
my $response = shift;
};
This hook was named after_error_render in Dancer, both names currently are synonyms for
backward-compatibility.
"on_route_exception" is called when an exception has been caught, at the route level, just
before rethrowing it higher. This hook receives a Dancer2::Core::App and the error as
arguments.
hook on_route_exception => sub {
my ($app, $error) = @_;
};
SESSIONS
Handling sessions
It's common to want to use sessions to give your web applications state; for instance,
allowing a user to log in, creating a session, and checking that session on subsequent
requests.
By default Dancer 2 has Simple sessions enabled. It implements a very simple in-memory
session storage. This will be fast and useful for testing, but such sessions will not
persist between restarts of your app.
If you'd like to use a different session engine you must declare it in the configuration
file.
For example to use YAML file base sessions you need to add the following to your
config.yml:
session: YAML
Or, to enable session support from within your code,
set session => 'YAML';
(However, controlling settings is best done from your config file.)
The Dancer2::Session::YAML backend implements a file-based YAML session storage to help
with debugging, but shouldn't be used on production systems.
There are other session backends, such as Dancer2::Session::Memcached, which are
recommended for production use.
You can then use the session keyword to manipulate the session:
Storing data in the session
Storing data in the session is as easy as:
session varname => 'value';
Retrieving data from the session
Retrieving data from the session is as easy as:
session('varname')
Or, alternatively,
session->read("varname")
Controlling where sessions are stored
For disc-based session backends like Dancer2::Session::YAML, session files are written to
the session dir specified by the "session_dir" setting, which defaults to "./sessions" if
not specifically set.
If you need to control where session files are created, you can do so quickly and easily
within your config file, for example:
session: YAML
engines:
session:
YAML:
session_dir: /tmp/dancer-sessions
If the directory you specify does not exist, Dancer2 will attempt to create it for you.
Changing session ID
If you wish to change the session ID (for example on privilege level change):
my $new_session_id = app->change_session_id
Destroying a session
When you're done with your session, you can destroy it:
app->destroy_session
Sessions and logging in
A common requirement is to check the user is logged in, and, if not, require them to log
in before continuing.
This can easily be handled using a before hook to check their session:
use Dancer2;
set session => "Simple";
hook before => sub {
if (!session('user') && request->path !~ m{^/login}) {
forward '/login', { requested_path => request->path };
}
};
get '/' => sub { return "Home Page"; };
get '/secret' => sub { return "Top Secret Stuff here"; };
get '/login' => sub {
# Display a login page; the original URL they requested is available as
# query_parameters->get('requested_path'), so could be put in a hidden field in the form
template 'login', { path => query_parameters->get('requested_path') };
};
post '/login' => sub {
# Validate the username and password they supplied
if (body_parameters->get('user') eq 'bob' && body_parameters->get('pass') eq 'letmein') {
session user => body_parameters->get('user');
redirect body_parameters->get('path') || '/';
} else {
redirect '/login?failed=1';
}
};
dance();
Here is what the corresponding "login.tt" file should look like. You should place it in a
directory called "views/":
<html>
<head>
<title>Session and logging in</title>
</head>
<body>
<form action='/login' method='POST'>
User Name : <input type='text' name='user'/>
Password: <input type='password' name='pass' />
<!-- Put the original path requested into a hidden
field so it's sent back in the POST and can be
used to redirect to the right page after login -->
<input type='hidden' name='path' value='<% path %>'/>
<input type='submit' value='Login' />
</form>
</body>
</html>
Of course, you'll probably want to validate your users against a database table, or maybe
via IMAP/LDAP/SSH/POP3/local system accounts via PAM etc. Authen::Simple is probably a
good starting point here!
A simple working example of handling authentication against a database table yourself
(using Dancer2::Plugin::Database which provides the "database" keyword, and
Crypt::SaltedHash to handle salted hashed passwords (well, you wouldn't store your users
passwords in the clear, would you?)) follows:
post '/login' => sub {
my $user_value = body_parameters->get('user');
my $pass_value = body_parameters->get('pass');
my $user = database->quick_select('users',
{ username => $user_value }
);
if (!$user) {
warning "Failed login for unrecognised user $user_value";
redirect '/login?failed=1';
} else {
if (Crypt::SaltedHash->validate($user->{password}, $pass_value))
{
debug "Password correct";
# Logged in successfully
session user => $user;
redirect body_parameters->get('path') || '/';
} else {
debug("Login failed - password incorrect for " . $user_value);
redirect '/login?failed=1';
}
}
};
Retrieve complete hash stored in session
Get complete hash stored in session:
my $hash = session;
Writing a session engine
In Dancer 2, a session backend consumes the role Dancer2::Core::Role::SessionFactory.
The following example using the Redis session demonstrates how session engines are written
in Dancer 2.
First thing to do is to create the class for the session engine, we'll name it
"Dancer2::Session::Redis":
package Dancer2::Session::Redis;
use Moo;
with 'Dancer2::Core::Role::SessionFactory';
we want our backend to have a handle over a Redis connection. To do that, we'll create an
attribute "redis"
use JSON;
use Redis;
use Dancer2::Core::Types; # brings helper for types
has redis => (
is => 'rw',
isa => InstanceOf['Redis'],
lazy => 1,
builder => '_build_redis',
);
The lazy attribute says to Moo that this attribute will be built (initialized) only when
called the first time. It means that the connection to Redis won't be opened until
necessary.
sub _build_redis {
my ($self) = @_;
Redis->new(
server => $self->server,
password => $self->password,
encoding => undef,
);
}
Two more attributes, "server" and "password" need to be created. We do this by defining
them in the config file. Dancer2 passes anything defined in the config to the engine
creation.
# config.yml
...
engines:
session:
Redis:
server: foo.mydomain.com
password: S3Cr3t
The server and password entries are now passed to the constructor of the Redis session
engine and can be accessed from there.
has server => (is => 'ro', required => 1);
has password => (is => 'ro');
Next, we define the subroutine "_retrieve" which will return a session object for a
session ID it has passed. Since in this case, sessions are going to be stored in Redis,
the session ID will be the key, the session the value. So retrieving is as easy as doing
a get and decoding the JSON string returned:
sub _retrieve {
my ($self, $session_id) = @_;
my $json = $self->redis->get($session_id);
my $hash = from_json( $json );
return bless $hash, 'Dancer2::Core::Session';
}
The "_flush" method is called by Dancer when the session needs to be stored in the
backend. That is actually a write to Redis. The method receives a "Dancer2::Core::Session"
object and is supposed to store it.
sub _flush {
my ($self, $session) = @_;
my $json = encode_json( { %{ $session } } );
$self->redis->set($session->id, $json);
}
For the "_destroy" method which is supposed to remove a session from the backend, deleting
the key from Redis is enough.
sub _destroy {
my ($self, $session_id) = @_;
$self->redis->del($session_id);
}
The "_sessions" method which is supposed to list all the session IDs currently stored in
the backend is done by listing all the keys that Redis has.
sub _sessions {
my ($self) = @_;
my @keys = $self->redis->keys('*');
return \@keys;
}
The session engine is now ready.
The Session keyword
Dancer2 maintains two session layers.
The first layer, Dancer2::Core::Session provides a session object which represents the
current session. You can read from it as many times as you want, and write to it as many
times as you want.
The second layer is the session engine (Dancer2::Session::Simple is one example), which is
used in order to implement the reading and writing from the actual storage. This is read
only once, when a request comes in (using a cookie whose value is "dancer.session" by
default). At the end of a request, all the data you've written will be flushed to the
engine itself, which will do the actual write to the storage (whether it's in a hash in
memory, in Memcache, or in a database).
TEMPLATES
Returning plain content is all well and good for examples or trivial apps, but soon you'll
want to use templates to maintain separation between your code and your content. Dancer2
makes this easy.
Your route handlers can use the template keyword to render templates.
Views
In Dancer2, a file which holds a template is called a view. Views are located in the
"appdir/views" directory.
You can change this location by changing the setting 'views'. For instance if your
templates are located in the 'templates' directory, do the following:
set views => path( app->location , 'templates' );
By default, the internal template engine Dancer2::Template::Simple is used, but you may
want to upgrade to Template Toolkit <http://www.template-toolkit.org/>. If you do so, you
have to enable this engine in your settings as explained in
Dancer2::Template::TemplateToolkit and you'll also have to install the Template module.
In order to render a view, just call the template keyword at the end of the action by
giving the view name and the HASHREF of tokens to interpolate in the view (note that for
convenience, the request, session, params and vars are automatically accessible in the
view, named "request", "session", "params", and "vars") - for example:
hook before => sub { var time => scalar(localtime) };
get '/hello/:name' => sub {
my $name = route_parameters->get('name');
template 'hello.tt', { name => $name };
};
The template "hello.tt" could contain, for example:
<p>Hi there, [% name %]!</p>
<p>You're using [% request.user_agent %]</p>
[% IF session.username %]
<p>You're logged in as [% session.username %]</p>
[% END %]
It's currently [% vars.time %]
For a full list of the tokens automatically added to your template (like "session",
"request", and "vars", refer to Dancer2::Core::Role::Template).
By default, views use a .tt extension. This can be overridden by setting the "extension"
attribute in the template engine configuration:
set engines => {
template => {
template_toolkit => {
extension => 'foo',
},
},
};
Layouts
A layout is a special view, located in the layouts directory (inside the views directory)
which must have a token named "content". That token marks the place where to render the
action view. This lets you define a global layout for your actions, and have each
individual view contain only specific content. This is a good thing and helps avoid lots
of needless duplication of HTML. :)
For example, the layout views/layouts/main.tt:
<html>
<head>...</head>
<body>
<div id="header">
...
</div>
<div id="content">
[% content %]
</div>
</body>
</html>
You can tell your app which layout to use with "layout: name" in the config file, or
within your code:
set layout => 'main';
You can control which layout to use (or whether to use a layout at all) for a specific
request without altering the layout setting by passing an options hashref as the third
param to the template keyword:
template 'index.tt', {}, { layout => undef };
If your application is not mounted under root ("/"), you can use a
"before_template_render" hook instead of hardcoding the path into your application for
your CSS, images and JavaScript:
hook before_template_render => sub {
my $tokens = shift;
$tokens->{uri_base} = request->base->path;
};
Then in your layout, modify your CSS inclusion as follows:
<link rel="stylesheet" href="[% uri_base %]/css/style.css" />
From now on you can mount your application wherever you want, without any further
modification of the CSS inclusion.
Encoding
If you use Plack and have a Unicode problem with your Dancer2 application, don't forget to
check if you have set your template engine to use Unicode, and set the default charset to
UTF-8. So, if you are using template toolkit, your config file will look like this:
charset: UTF-8
engines:
template:
template_toolkit:
ENCODING: utf8
Default Template Variables
Every template knows about the following variables, which are provided by
Dancer2::Core::Role::Template. Some are similar to the keywords you can use in the Perl
part of your Dancer2 application.
• perl_version
Current version of perl, effectively $^V
<http://perldoc.perl.org/perlvar.html#%24%5eV>.
• dancer_version
Current version of Dancer2, effectively "Dancer2->VERSION".
• settings
A hash of the application configuration. This is like the config keyword.
• request
The current request object. This is like the request keyword.
• params
A hash reference of all the parameters.
Currently the equivalent of "$request->params", and like the params keyword.
• vars
The list of request variables, which is what you would get if you called the vars
keyword.
• session
The current session data, if a session exists. This is like the session keyword.
STATIC FILES
Static Directory
Static files are served from the ./public directory. You can specify a different location
by setting the "public_dir" option:
set public_dir => path( app->location , 'static' );
When you modify default public_dir you have to set "static_handler" option.
set static_handler => true;
Note that the public directory name is not included in the URL. A file
./public/css/style.css is made available as <http://example.com/css/style.css>.
Static File from a Route Handler
It's possible for a route handler to send a static file, as follows:
get '/download/*' => sub {
my ($file) = splat;
send_file $file;
};
Or even if you want your index page to be a plain old index.html file, just do:
get '/' => sub {
send_file '/index.html'
};
FILE UPLOADS
Files are uploaded in Dancer2 using the class Dancer2::Core::Request::Upload. The objects
are accessible within the route handlers using the "upload" keyword:
post '/upload' => sub {
my $upload = upload('file_input_name'); # upload object
$upload->copy_to('Uploads/');
};
CONFIGURATION
Configuration and environments
Configuring a Dancer2 application can be done in many ways. The easiest one (and maybe the
dirtiest) is to put all your settings statements at the top of your script, before calling
the "dance()" method.
Other ways are possible: for example, you can define all your settings in the file
"appdir/config.yml". For this, you must have installed the YAML module, and of course,
write the config file in YAML.
That's better than the first option, but it's still not perfect as you can't switch easily
from an environment to another without rewriting the config file.
A better solution is to have one config.yml file with default global settings, like the
following:
# appdir/config.yml
logger: 'file'
layout: 'main'
And then write as many environment files as you like in "appdir/environments". That way,
the appropriate environment config file will be loaded according to the running
environment (if none is specified, it will be 'development').
You can change the running environment when starting your app using the "plackup"
command's "--env" or "--E" switch:
plackup -E production bin/app.psgi
Altenatively, you can set the "DANCER_ENVIRONMENT"
<https://metacpan.org/pod/Dancer2::Config#DANCER_ENVIRONMENT> environment variable in the
shell or in your web server's configuration file.
Typically, you'll want to set the following values in a development config file:
# appdir/environments/development.yml
log: 'debug'
startup_info: 1
show_stacktrace: 1
And in a production one:
# appdir/environments/production.yml
log: 'warning'
startup_info: 0
show_stacktrace: 0
Please note that you are not limited to writing configuration files in YAML. Dancer2
supports any file format that is supported by Config::Any, such as JSON, XML, INI files,
and Apache-style config files. See the Dancer2 configuration guide
<https://metacpan.org/pod/Dancer2::Config#MANIPULATING-SETTINGS-VIA-CONFIGURATION-FILES>
for more information.
Accessing configuration information
A Dancer2 application can use the "config" keyword to easily access the settings within
its config file, for instance:
get '/appname' => sub {
return "This is " . config->{appname};
};
This makes keeping your application's settings all in one place simple and easy - you
shouldn't need to worry about implementing all that yourself. :)
Settings
It's possible to change almost every parameter of the application via the settings
mechanism.
A setting is a key/value pair assigned by the keyword set:
set setting_name => 'setting_value';
More usefully, settings can be defined in a configuration file. Environment-specific
settings can also be defined in environment-specific files (for instance, you do not want
to show error stacktraces in production, and might want extra logging in development).
Serializers
When writing a webservice, data serialization/deserialization is a common issue to deal
with. Dancer2 can automatically handle that for you, via a serializer.
When setting up a serializer, a new behaviour is authorized for any route handler you
define: any non-scalar response will be rendered as a serialized string, via the current
serializer.
Here is an example of a route handler that will return a hashref:
use Dancer2;
set serializer => 'JSON';
get '/user/:id/' => sub {
{ foo => 42,
number => 100234,
list => [qw(one two three)],
}
};
Dancer2 will render the response via the current serializer.
Hence, with the JSON serializer set, the route handler above would result in a content
like the following:
{"number":100234,"foo":42,"list":["one","two","three"]}
If you send a value which is validated serialized data, but is not in the form a key and
value pair (such as a serialized string or a JSON array), the data will not be available
in "params" but will be available in "request->data".
The following serializers are available, be aware they dynamically depend on Perl modules
you may not have on your system.
• JSON
Requires JSON.
• YAML
Requires YAML,
• XML
Requires XML::Simple.
• Mutable
Will try to find the appropriate serializer using the Content-Type and Accept-type
header of the request.
Importing using Appname
An app in Dancer2 uses the class name (defined by the "package" function) to define the
App name. Thus separating the App to multiple files, actually means creating multiple
applications. This means that any engine defined in an application, because the
application is a complete separate scope, will not be available to a different
application:
package MyApp::User {
use Dancer2;
set serializer => 'JSON';
get '/view' => sub {...};
}
package MyApp::User::Edit {
use Dancer2;
get '/edit' => sub {...};
}
These are two different Dancer2 Apps. They have different scopes, contexts, and thus
different engines. While "MyApp::User" has a serializer defined, "MyApp::User::Edit" will
not have that configuration.
By using the import option "appname", we can ask Dancer2 to extend an App without creating
a new one:
package MyApp::User {
use Dancer2;
set serializer => 'JSON';
get '/view' => sub {...};
}
package MyApp::User::Edit {
use Dancer2 appname => 'MyApp::User'; # extending MyApp::User
get '/edit' => sub {...};
}
The import option "appname" allows you to seamlessly extend Dancer2 Apps without creating
unnecessary additional applications or repeat any definitions. This allows you to spread
your application routes across multiple files and allow ease of mind when developing it,
and accommodate multiple developers working on the same codebase.
# app.pl
use MyApp::User;
use MyApp::User::Edit;
# single application composed of routes provided in multiple files
MyApp::User->to_app;
This way only one class needs to be loaded while creating an app:
# app.pl:
use MyApp::User;
MyApp::User->to_app;
LOGGING
Configuring logging
It's possible to log messages generated by the application and by Dancer2 itself.
To start logging, select the logging engine you wish to use with the "logger" setting;
Dancer2 includes built-in log engines named "file" and "console", which log to a logfile
and to the console respectively.
To enable logging to a file, add the following to your config file:
logger: 'file'
Then you can choose which kind of messages you want to actually log:
log: 'core' # will log debug, info, warnings, errors,
# and messages from Dancer2 itself
log: 'debug' # will log debug, info, warning and errors
log: 'info' # will log info, warning and errors
log: 'warning' # will log warning and errors
log: 'error' # will log only errors
If you're using the "file" logging engine, a directory "appdir/logs" will be created and
will host one logfile per environment. The log message contains the time it was written,
the PID of the current process, the message and the caller information (file and line).
Logging your own messages
Just call debug <https://metacpan.org/pod/Dancer2::Manual#debug>, info
<https://metacpan.org/pod/Dancer2::Manual#info>, warning
<https://metacpan.org/pod/Dancer2::Manual#warning> or error
<https://metacpan.org/pod/Dancer2::Manual#error> with your message:
debug "This is a debug message from my app.";
TESTING
Using Plack::Test
Plack::Test receives a common web request (using standard HTTP::Request objects), fakes a
web server in order to create a proper PSGI request, and sends it to the web application.
When the web application returns a PSGI response (which Dancer applications do), it will
then convert it to a common web response (as a standard HTTP::Response object).
This allows you to then create requests in your test, create the code reference for your
web application, call them, and receive a response object, which can then be tested.
Basic Example
Assuming there is a web application:
# MyApp.pm
package MyApp;
use Dancer2;
get '/' => sub {'OK'};
1;
The following test base.t is created:
# base.t
use strict;
use warnings;
use Test::More tests => 2;
use Plack::Test;
use HTTP::Request;
use MyApp;
Creating a coderef for the application using the "to_app" keyword:
my $app = MyApp->to_app;
Creating a test object from Plack::Test for the application:
my $test = Plack::Test->create($app);
Creating the first request object and sending it to the test object to receive a response:
my $request = HTTP::Request->new( GET => '/' );
my $response = $test->request($request);
It can now be tested:
ok( $response->is_success, '[GET /] Successful request' );
is( $response->content, 'OK', '[GET /] Correct content' );
Putting it together
# base.t
use strict;
use warnings;
use Test::More;
use Plack::Test;
use HTTP::Request::Common;
use MyApp;
my $test = Plack::Test->create( MyApp->to_app );
my $response = $test->request( GET '/' );
ok( $response->is_success, '[GET /] Successful request' );
is( $response->content, 'OK', '[GET /] Correct content' );
done_testing();
Subtests
Tests can be separated using Test::More's "subtest" functionality, thus creating multiple
self-contained tests that don't overwrite each other.
Assuming we have a different app that has two states we want to test:
# MyApp.pm
package MyApp;
use Dancer2;
set serializer => 'JSON';
get '/:user' => sub {
my $user = route_parameters->get('user');
$user and return { user => $user };
return {};
};
1;
This is a contrived example of a route that checks for a user parameter. If it exists, it
returns it in a hash with the key 'user'. If not, it returns an empty hash
# param.t
use strict;
use warnings;
use Test::More;
use Plack::Test;
use HTTP::Request::Common;
use MyApp;
my $test = Plack::Test->create( MyApp->to_app );
subtest 'A empty request' => sub {
my $res = $test->request( GET '/' );
ok( $res->is_success, 'Successful request' );
is( $res->content '{}', 'Empty response back' );
};
subtest 'Request with user' => sub {
my $res = $test->request( GET '/?user=sawyer_x' );
ok( $res->is_success, 'Successful request' );
is( $res->content '{"user":"sawyer_x"}', 'Empty response back' );
};
done_testing();
Cookies
To handle cookies, which are mostly used for maintaining sessions, the following modules
can be used:
• Test::WWW::Mechanize::PSGI
• LWP::Protocol::PSGI
• HTTP::Cookies
Taking the previous test, assuming it actually creates and uses cookies for sessions:
# ... all the use statements
use HTTP::Cookies;
my $jar = HTTP::Cookies->new;
my $test = Plack::Test->create( MyApp->to_app );
subtest 'A empty request' => sub {
my $res = $test->request( GET '/' );
ok( $res->is_success, 'Successful request' );
is( $res->content '{}', 'Empty response back' );
$jar->extract_cookies($res);
ok( $jar->as_string, 'We have cookies!' );
};
subtest 'Request with user' => sub {
my $req = GET '/?user=sawyer_x';
$jar->add_cookie_header($req);
my $res = $test->request($req);
ok( $res->is_success, 'Successful request' );
is( $res->content '{"user":"sawyer_x"}', 'Empty response back' );
$jar->extract_cookies($res);
ok( ! $jar->as_string, 'All cookies deleted' );
};
done_testing();
Here a cookie jar is created, all requests and responses, existing cookies, as well as
cookies that were deleted by the response, are checked.
Accessing the configuration file
By importing Dancer2 in the command line scripts, there is full access to the
configuration using the imported keywords:
use strict;
use warnings;
use Test::More;
use Plack::Test;
use HTTP::Request::Common;
use MyApp;
use Dancer2;
my $appname = config->{'appname'};
diag "Testing $appname";
# ...
PACKAGING
Carton
What it does
Carton sets up a local copy of your project prerequisites. You only need to define them in
a file and ask Carton to download all of them and set them up. When you want to deploy
your app, you just carry the git clone and ask Carton to set up the environment again and
you will then be able to run it.
The benefits are multifold:
• Local Directory copy
By putting all the dependencies in a local directory, you can make sure they aren't
updated by someone else by accident and their versions locked to the version you
picked.
• Sync versions
Deciding which versions of the dependent modules your project needs allows you to sync
this with other developers as well. Now you're all using the same version and they
don't change unless you want update the versions you want. When updated everyone again
uses the same new version of everything.
• Carry only the requirement, not bundled modules
Instead of bundling the modules, you only actually bundle the requirements. Carton
builds them for you when you need it.
Setting it up
First set up a new app:
$ dancer2 gen -a MyApp
...
Delete the files that are not needed:
$ rm -f Makefile.PL MANIFEST MANIFEST.SKIP
Create a git repo:
$ git init && git add . && git commit -m "initial commit"
Add a requirement using the cpanfile format:
$ cat > cpanfile
requires 'Dancer2' => 0.155000;
requires 'Template' => 0;
recommends 'URL::Encode::XS' => 0;
recommends 'CGI::Deurl::XS' => 0;
recommends 'HTTP::Parser::XS' => 0;
Ask carton to set it up:
$ carton install
Installing modules using [...]
Successfully installed [...]
...
Complete! Modules were install into [...]/local
Now we have two files: cpanfile and cpanfile.snapshot. We add both of them to our Git
repository and we make sure we don't accidentally add the local/ directory Carton created
which holds the modules it installed:
$ echo local/ >> .gitignore
$ git add .gitignore cpanfile cpanfile.snapshot
$ git commit -m "Start using carton"
When we want to update the versions on the production machine, we simply call:
$ carton install --deployment
By using --deployment we make sure we only install the modules we have in our
cpanfile.snapshot file and do not fallback to querying the CPAN.
FatPacker
App::FatPacker (using its command line interface, fatpack) packs dependencies into a
single file, allowing you to carry a single file instead of a directory tree.
As long as your application is pure-Perl, you could create a single file with your
application and all of Dancer2 in it.
The following example will demonstrate how this can be done:
Assuming we have an application in lib/MyApp.pm:
package MyApp;
use Dancer2;
get '/' => sub {'OK'};
1;
And we have a handler in bin/app.pl:
use strict;
use warnings;
use FindBin;
use lib "$FindBin::Bin/../lib";
use MyApp;
MyApp->to_app;
To fatpack it, we begin by tracing the script:
$ fatpack trace bin/app.pl
This creates a fatpacker.trace file. From this we create the packlists:
$ fatpack packlists-for `cat fatpacker.trace` > packlists
The packlists are stored in a file called packlists.
Now we create the tree using the following command:
$ fatpack tree `cat packlists`
The tree is created under the directory fatlib.
Now we create a file containing the dependency tree, and add our script to it, using the
following command:
$ (fatpack file; cat bin/app.pl) > myapp.pl
This creates a file called myapp.pl with everything in it. Dancer2 uses MIME::Types which
has a database of all MIME types and helps translate those. The small database file
containing all of these types is a binary and therefore cannot be fatpacked. Hence, it
needs to be copied to the current directory so our script can find it:
$ cp fatlib/MIME/types.db .
MIDDLEWARES
Plack middlewares
If you want to use Plack middlewares, you need to enable them using Plack::Builder as
such:
# in app.psgi or any other handler
use MyApp;
use Plack::Builder;
builder {
enable 'Deflater';
enable 'Session', store => 'File';
enable 'Debug', panels => [ qw<DBITrace Memory Timer> ];
MyApp->to_app;
};
The nice thing about this setup is that it will work seamlessly through Plack or through
the internal web server.
# load dev web server (without middlewares)
perl -Ilib app.psgi
# load plack web server (with middlewares)
plackup -I lib app.psgi
You do not need to provide different files for either server.
Path-based middlewares
If you want to set up a middleware for a specific path, you can do that using
Plack::Builder which uses Plack::App::URLMap:
# in your app.psgi or any other handler
use MyApp;
use Plack::Builder;
my $special_handler = sub { ... };
builder {
mount '/special' => $special_handler;
mount '/' => MyApp->to_app;
};
Removing default middlewares
By default, a Dancer2 app is automatically wrapped with the following middleware
• Plack::Middleware::FixMissingBodyInRedirect
• Plack::Middleware::Head
You can configure the setting "no_default_middleware" to a true value to stop your Dancer2
app being wrapped with these default middleware layers.
# in you Dancer2 app or config.yml
package MyApp;
use Dancer2
set no_default_middleware => true;
This is necessary if you need to add eTag or ContentMD5 headers to "HEAD" requests, and
you are encouraged to manually add those default middleware back into your PSGI stack.
Running on Perl web servers with plackup
A number of Perl web servers supporting PSGI are available on CPAN:
• Starman
"Starman" is a high performance web server, with support for preforking, signals,
multiple interfaces, graceful restarts and dynamic worker pool configuration.
• Twiggy
"Twiggy" is an "AnyEvent" web server, it's light and fast.
• Corona
"Corona" is a "Coro" based web server.
To start your application, just run plackup (see Plack and specific servers above for all
available options):
$ plackup bin/app.psgi
$ plackup -E deployment -s Starman --workers=10 -p 5001 -a bin/app.psgi
As you can see, the scaffolded Perl script for your app can be used as a PSGI startup
file.
Enabling content compression
Content compression (gzip, deflate) can be easily enabled via a Plack middleware (see
"Plack::Middleware" in Plack): Plack::Middleware::Deflater. It's a middleware to encode
the response body in gzip or deflate, based on the "Accept-Encoding" HTTP request header.
Enable it as you would enable any Plack middleware. First you need to install
Plack::Middleware::Deflater, then in the handler (usually app.psgi) edit it to use
Plack::Builder, as described above:
use Dancer2;
use MyApp;
use Plack::Builder;
builder {
enable 'Deflater';
MyApp->to_app;
};
To test if content compression works, trace the HTTP request and response before and after
enabling this middleware. Among other things, you should notice that the response is gzip
or deflate encoded, and contains a header "Content-Encoding" set to "gzip" or "deflate".
Running multiple apps with Plack::Builder
You can use Plack::Builder to mount multiple Dancer2 applications on a PSGI webserver like
Starman.
Start by creating a simple app.psgi file:
use OurWiki; # first app
use OurForum; # second app
use Plack::Builder;
builder {
mount '/wiki' => OurWiki->to_app;
mount '/forum' => OurForum->to_app;
};
and now use Starman
plackup -a app.psgi -s Starman
Currently this still demands the same appdir for both (default circumstance) but in a
future version this will be easier to change while staying very simple to mount.
Running from Apache with Plack
You can run your app from Apache using PSGI (Plack), with a config like the following:
<VirtualHost myapp.example.com>
ServerName www.myapp.example.com
ServerAlias myapp.example.com
DocumentRoot /websites/myapp.example.com
<Directory /home/myapp/myapp>
AllowOverride None
Order allow,deny
Allow from all
</Directory>
<Location />
SetHandler perl-script
PerlResponseHandler Plack::Handler::Apache2
PerlSetVar psgi_app /websites/myapp.example.com/app.psgi
</Location>
ErrorLog /websites/myapp.example.com/logs/error_log
CustomLog /websites/myapp.example.com/logs/access_log common
</VirtualHost>
To set the environment you want to use for your application (production or development),
you can set it this way:
<VirtualHost>
...
SetEnv DANCER_ENVIRONMENT "production"
...
</VirtualHost>
PLUGINS
Writing a plugin
See "Writing the plugin" in Dancer2::Plugin for information on how to author a new plugin
for Dancer2.
EXPORTS
By default, "use Dancer2" exports all the DSL keywords and sets up the webapp under the
name of the current package. The following tags control exports and webapp namespace.
• !keyword
If you want to prevent Dancer2 from exporting specific keywords (perhaps you plan to
implement them yourself in a different way, or they clash with another module you're
loading), you can simply exclude them:
use Test::More;
use Dancer2 qw(!pass);
The above would import all keywords as usual, with the exception of "pass".
• appname
A larger application may split its source between several packages to aid
maintainability. Dancer2 will create a separate application for each package, each
having separate hooks, config and/or engines. You can force Dancer2 to collect the
route and hooks into a single application with the "appname" tag; e.g.
package MyApp;
use Dancer2;
get '/foo' => sub {...};
package MyApp::Private;
use Dancer2 appname => MyApp;
get '/bar' => sub {...};
The above would add the "bar" route to the MyApp application. Dancer2 will not create
an application with the name "MyApp::Private".
• :nopragmas
By default Dancer2 will import three pragmas: strict, warnings, and utf8. If you
require control over the imported pragmas, you can add :nopragmas to the importing
flags, in which case Dancer2 will not import any pragmas:
use strict;
use warnings;
no warnings 'experimental::smartmatch'; # for example...
use Dancer2 ':nopragmas'; # do not touch the existing pragmas
This way importing "Dancer2" does not change the existing pragmas setup you have.
When you "use Dancer2", you get an "import" method added into the current package. This
will override previously declared import methods from other sources, such as Exporter.
Dancer2 applications support the following tags on import:
• with
The "with" tag allows an app to pass one or more config entries to another app, when
it "use"s it.
package MyApp;
use Dancer2;
BEGIN { set session => 'YAML' };
use Blog with => { session => engine('session') };
In this example, the session engine is passed to the "Blog" app. That way, anything
done in the session will be shared between both apps.
Anything that is defined in the config entry can be passed that way. If we want to
pass the whole config object, it can be done like so:
use SomeApp with => { %{config()} };
DSL KEYWORDS
Dancer2 provides you with a DSL (Domain-Specific Language) which makes implementing your
web application trivial.
For example, take the following example:
use Dancer2;
get '/hello/:name' => sub {
my $name = route_parameters->get('name');
};
dance;
"get" and "route_parameters" are keywords provided by Dancer2.
See "DSL Keywords manual" in Dancer2::Manual::Keywords for a complete list of keywords
provided by Dancer2.
AUTHOR
Dancer Core Developers
COPYRIGHT AND LICENSE
This software is copyright (c) 2023 by Alexis Sukrieh.
This is free software; you can redistribute it and/or modify it under the same terms as
the Perl 5 programming language system itself.